The present invention generally relates to a radiant heater or stove and, more particularly, to a heating drum adapted to seat over a burner of the radiant heater or stove for enhancing the heating of the combustion gas at lower ambient air temperature with high radiant efficiency.
The prior art heating drum so far found closest to the present invention is disclosed in the U.S. Pat. No. 1,037,306, patented on Sept. 3, 1912. The heating drum disclosed therein is shown as comprising an axially corrugated barrel having one end obviously closed and provided with a handle and the other end formed integrally with a hood adapted to seat over the burner, said hood having a downwardly flared flange integral therewith. The barrel so axially corrugated forms therein a generally cylindrical inner chamber and a plurality of axially equally spaced annular chambers communicated with the cylindrical inner chamber and alternating with concave spaces over the length thereof. For throwing heating air inside the heating drum off therefrom, the barrel is provided with gas outlet openings. These gas outlet openings are, according to the patent now under discussion, defined on the outermost periphery of each of the walls defining the respective annular chambers and opened in a direction essentially perpendicular to the longitudinal axis of the barrel.
The patent in question also discloses the side openings defined in the downwardly flared flange so as to open diagonally upwards for the introduction of air exteriorly of the heating drum into the interior of the heating drum during the combustion of fuel taking place in the burner.
It appears that the above mentioned patent has been directed to an improvement of a perforated heating drum of right cylinder in shape for the purpose of enabling a relatively large space to be heated in a relatively short time by forcing the heated air inside the barrel to be thrown out through the gas outlet openings in a direction radially and outwardly of the heating drum. Considering the particular location of the gas outlet openings in the heating drum and also the presumed, but obvious purpose for which it has been provided, taken together with the illustrated longitudinal sectional representation of the annular chambers, each of the gas outlet openings is obviously so positioned and so oriented that the heated gas inside the barrel can be thrown out through the respective gas outlet opening at a high speed as if a fluid medium were force outwards from a nozzle. As is well known to those skilled in the art, any fluid medium emerging outwards through any constricted opening draws the ambient air to meet with it. This phenomenon takes place even in the heated gas stream emerging outwardly each gas outlet opening, with the consequence that the thermal boundary layer is so reduced in thickness as to result in the retarded heating of the heating drum itself, although the heated gas appears to reach a relatively long distance.
Moreover, since the side openings in the downwardly flared flange are utilized to draw the ambient air into the interior of the heating drum to mix with the products of combustion prior to being emitted to the outside through each gas outlet opening, the heated gas inside the heating drum tends to be inevitably cooled in admixture with the fresh air introduced thereinto through the side openings and, therefore, it is quite obvious that the temperature of the heating drum tends to be reduced correspondingly.
It is to be noted that, if the temperature of the surface from which heat energy is radiated is low, a given load of combustion energy will not be efficiently converted into radiant energy as is the case with the convection heating system. Furthermore, when it comes to the corrugated or bellows-like heating drum, the upflow current of heated gas tends to receive a relatively great resistance and, accordingly, unless care is taken such as embodied in the present invention, the heated gas inside the heating drum tends to be distributed unevenly inside the heating drum with the result that a lower portion of the drum adjacent to the burner will be excessively heated as compared with the other portion thereof.
Although less pertinent to the present invention, another U.S. Pat. No.4,140,100, patented on Feb. 20, 1979, discloses a radiant heater of horizontal model wherein a horizontally lying doubled heating cylinder assembly is employed with the burner assembly positioned adjacent to one end thereof. The doubled heating cylinder assembly disclosed therein comprises perforated outer and inner cylinders coaxially positioned one inside the other, the perforations in the outer cylinder being arranged out of alignment with and in offset relation to the perforations in the inner cylinder in a direction both circumferentially and axially of the heating cylinder assembly.
In view of the horizontal model susceptible to the problem in which the central portion of the heating cylinder assembly is more difficult to heat than the opposite end portions thereof, the last mentioned patent discloses the recommended arrangement of the perforations in the inner cylinder wherein the ratio of the total open area of the perforations bored at the central portion of the inner cylinder to the open area is higher than that at each end portion thereof for the purpose of facilitating blow off through the perforations of the combustion flame which in turn impinges upon the non-perforated wall of the outer cylinder. As one method to achieve this, it suggests the employment of the perforations in the inner cylinder in a greater number per unit area at the central portion thereof than that at each end portion, the employment of the perforations of greater diameter at the central portion thereof than that of each end portion, and the employment of the perforations of which diameters gradually increase towards the central portion of the inner cylinder.